Abstract
Apoptotic resistance of cancer cells may be overcome by the combination of treatments that activate the two major apoptotic pathways: (i) the death receptor pathway activated by death ligands and (ii) the DNA damage pathway activated by chemotherapy. We have previously shown that mesothelioma cells, resistant to most treatments, are sensitive to the combination of the death ligand tumor necrosis factor-related apoptosis inducing ligand (TRAIL/Apo2L) plus chemotherapy. We investigated a possible role for c-Jun N-terminal kinase (JNK) in the synergistic effect, knowing that JNK can be activated separately by TRAIL and by DNA damage. We chose to study the M28 and REN human mesothelioma cell lines, which are p53-inactivated, to avoid an interaction between p53 and JNK. We showed that JNK was activated by TRAIL and by etoposide and that the activation was enhanced by the combination of the two treatments. We found this activation to be caspase-independent. To inhibit the JNK pathway, we used either dominant-negative constructs of JNK1 and JNK2 (compared with dominant-negative caspase 9) or a chemical inhibitor of the JNK pathway (SP600125). In cells treated with TRAIL plus etoposide, JNK inhibition increased cell survival and decreased apoptosis significantly. In transfected M28 cells, the effect of JNK inhibition was as great as that of the dominant-negative caspase 9 construct. We conclude that JNK contributes to the synergistic effect of TRAIL combined with DNA damage by mediating signals independent of p53 leading to apoptosis.
Highlights
Defects in normal apoptotic programs contribute to the formation of tumors [1] and interfere with the tumor response to conventional therapy [2, 3]
Apoptotic resistance of cancer cells may be overcome by the combination of treatments that activate the two major apoptotic pathways: (i) the death receptor pathway activated by death ligands and (ii) the DNA damage pathway activated by chemotherapy
Jun N-terminal kinase (JNK) Is Activated in Mesothelioma Cells by TRAIL, Etoposide, and the Combination—To confirm that JNK can be activated in M28 and REN cell lines, we exposed the cells to UV light (40 J/m2) as a well characterized stimulus for JNK signaling and harvested them 30 min later to measure the phosphorylation of JNK and total JNK expression
Summary
Case of apoptotic stimuli, induction of JNK signaling has been proposed to enhance apoptotic responses to tumor necrosis factor [16] and to Fas [17, 18]. JNK signals could be important for synergistic apoptotic responses and, if so, could potentially be manipulated to potentiate cancer therapies. In part because mesothelioma is reported to express wild-type p53 [20], we investigated whether p53 was involved in either synergy or in a p53-dependent JNK activation. We found that these cells had nonfunctional p53. We asked whether JNK signals played a p53-independent role in the synergistic apoptotic responses. We describe a significant role for JNK signals in the synergistic apoptosis induced by TRAIL and the topoisomerase inhibitor, etoposide
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
